I don't think that 205 will hurt you at all, my main point, before I got off on tangents, was that I believe that the an engine should run within 5 (or 10) degrees of the thermostat temp, if it does not, then I believe this to be evidencethat the cooling system is working at capacity, which leaves very little room for anything to go wrong. I understand that this is a common issue on classic Mustangs, but this does not lessen it's importance.

As a side point, just because you have a mechanical guage, it's accuracy is not guaranteed, even if it's new,,, I know this to be a fact...